New genus started because outwardly identical animals are two different “species”

A “new departure,” we are tld, in the systematic classification of animals (taxonomy). From ScienceDaily:

Up until quite recently, the animal phylum Placozoa enjoyed a unique position in animal systematics. It was the only phylum to which only a single species had ever been assigned: Trichoplax adhaerens. Now, however, at team led by Professor Gert Wörheide of LMU’s Department of Earth and Environmental Sciences and GeoBio-Center has discovered that placozoan specimens collected from coastal waters off Hong Kong clearly differ from T. adhaerens in their genetic make-up. Indeed, the differences between the two are so striking that the Hong Kong population not only represents a new species but also has been assigned to a new genus — even though the two genera are morphologically indistinguishable. The definition of a new species and genus solely on the basis of comparative genomic data constitutes a new departure in the systematic classification of animals. The findings appear in PLOS Biology.

Placozoa are among the simplest known multicellular animals, lacking both muscles and nerve cells. They are only a few millimeters long and their cells are organized into two flat layers. They have been found in tropical and subtropical waters around the world. But, regardless of locality of origin, all placozoans have the same gross morphology and same basic cellular architecture. Since conventional approaches to the definition and differentiation of animal species rely on differences in overall body plans and detailed morphology, all placozoan specimens so far collected have been attributed to the species T. adhaerens, which was first described in 1883. “However, genetic data based on short DNA signature sequences that serve to distinguish species from one another had already suggested that placozoans exhibit a great deal of genetic diversity. And that in turn indicates that the phylum actually includes many different species,” says Wörheide.

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The authors of the new study believe that the placozoans may have undergone a very peculiar mode of evolution, in which speciation has occurred exclusively at the genetic level without notable morphological diversification. “We have some indications that point to the operation of negative selection, so it is possible that the development of morphological novelties may be repressed. But we are still very much at the beginning of the search for an explanation of this unique evolutionary trajectory,” says Eitel. Paper.(open access) – Eitel M, Francis WR, Varoqueaux F, Daraspe J, Osigus H-J, Krebs S, et al. Comparative genomics and the nature of placozoan species. PLoS Biol, 2018 DOI: 10.1371/journal.pbio.2005359 More.

To cut to the chase, the system is a mess. What does that say for theories like neo-Darwinism which are based on the mess and depend on its swirling currents?

See also: Speciation: A bread yeast and a yeast that causes infections turn out to be the same species

The concept of a “species,” as in On the Origin of Species, may well be in itself a dated idea, especially where fast-reproducing unicellular life forms are concerned. A measure that capture fluidity is needed.

4 Replies to “New genus started because outwardly identical animals are two different “species””

“Our first indication that forest cobras aren’t just a single species came when we sequenced the DNA of a few specimens that we thought were just different colour forms, and found enormous differences between them, far greater than between other cobra species,” said Wolfgang Wüster.

This is happening all the time. Long ago I said that whole genome analysis would either confirm, or throw into question, Darwinian orthodoxy. As they say, “the trend is your friend.” But not for Darwinism.

The fewer times you see something the less probable it is. The more times you see something the more probable it is. Learning things that I did not know before is one benefit of hanging out over at “The Skeptical Zone.”